1. Field of the Invention
The present invention generally relates to display systems capable of dynamically controlling a display refresh rate, and more particularly to a method and system of measuring quantitative changes in display frame content for dynamically controlling a display refresh rate.
2. Description of the Related Art
Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
The refresh rate of a display device is the frequency at which display frames are repainted on a display device. Each refresh cycle of the display screen usually involves a series of processing steps, including accessing image data of multiple image surfaces rendered and stored in a frame buffer and combining the image surfaces to form a composite display frame. In parallel, the video signals corresponding to the composite display frame are also driven to the display device to update each pixel onto the screen of the display device. “Tearing” and other visual artifacts can occur when the asynchronous steps of rendering/compositing a frame and scanning out pixels occur out of sync. To avoid these artifacts, visual computing devices typically do “flipping” wherein composition of new frame buffer contents is done in off-screen frame-buffer memory separate from the frame-buffer currently being scanned from, and then synchronize the scanning to begin on the new frame-buffer as the scan-out of the current frame-buffer has reached it's end. As these processing steps are repeated at a high frequency, they can consume significant amount of power.
For situations in which dynamic graphics contents are to be rendered on the screen, e.g., interactive 3D games where the frame buffer contents are switched at a high frequency, also referred to as a “high flipping rate”, a refresh rate of at least 60 Hz is usually necessary to completely convey the changing pixels without missing any visual content on the display screen. However, in other instances where the frame buffer updates are occurring at a low flipping rate, e.g., such as when the display screen represents an idle or quasi-static Windows Desktop image without any inputs or cursor movements by the user, it may be visually acceptable to reduce the refresh rate of the display screen to reduce the power consumption.
U.S. Application Publication No. 2006/0146056 describes one technical approach for dynamically controlling the refresh rate of a display device. This technical approach, also described as a “temporal entropy approach using intra-frame entropy detection”, detects significant rendering in a display frame by assessing a bounded area affected by the content updates. However, this approach involves a number of testing steps in software and hardware to detect the bounded area which does not exclude interference of small display surfaces such as cursors. To carry out these steps in a timely manner, additional hardware complexity is required and thus driving up the cost of implementing and validating this technical approach. In addition, this prior art approach does not measure quantitative changes in the content of a display frame and evaluate how these quantitative changes evolve over a period of time.
What is needed in the art is thus a method and system that can cost effectively and efficiently evaluate quantitative changes in the content frame rate and also evaluate how these changes evolve over a period of time for dynamically adjusting a display refresh rate and address at least the problems set forth above.